Conventional inspection of printouts has been performed manually. Recently, however, apparatuses for inspecting printouts have been used as post-processing of offset printing. In such inspection apparatuses, a printout is read for several times and an excellent read image is selected manually out of them, thereby generating a master image serving as a standard for inspection. A certain area of the generated master image is compared with a corresponding area of read image of the targeted printout for inspection. Depending on the level of the difference between the master image and the read image, defects on printouts are determined.
Digital printers such as electrophotographic printers that have become popular these days are good for printing a small number of copies or for variable printing in which printed contents often vary for each copy. For that reason, generating master images from printouts to be used for comparison inspection, in the same manner as the conventional offset printer, is inefficient. To address this issue, it can be considered to generate master images from print data. This can enable digital printers to correspond to variable printing efficiently.
In such image inspection processing, determination whether the printout is defective is performed as follows: align the positions of a read image generated by reading a printout sheet and a master image generated from print data, match the size of the read image and that of the master image, compare them with each other for each pixel therein to obtain the difference between the read image and the master image, and compare the difference and a predetermined threshold.
In such printout defect detection technologies, for inspecting the whole of the printout sheet, the printout sheet may be read in a larger area than the size of the printout sheet, thereby preventing the edges of the sheet from being excluded from the reading range of the sheet. In this case, the area outside of the sheet is displayed, i.e., the color of the surface of a conveying body such as a carriage belt that conveys the sheet is displayed on the end areas of the read image. The master image used for comparing with the read image therefore needs to be generated by adding the color of the surface of the carriage belt, for example, around the print data.
Another technology of inspection by comparing images is developed in which no-inspection areas are set for disabling determination as defective thereon when the difference from a standard image is found in a predetermined area (refer to PTL 1, for example).
By applying the above-described technology as disclosed in PTL 1 to the area outside of a document, the area outside of the document can be determined as a no-inspection area. This requires manual setting of such a no-inspection area, which may burden the users with manual operations.
In view of the foregoing, embodiments of the present invention aim to provide an image inspection in which a master image is compared with a read image generated by reading a printed output result of the image formation and output, which can readily determine an area outside of a document.